emBox

The emBox value represents the design space of the font and is used to place Chinese,
Korean, or Japanese glyphs relative to the Roman baseline.
Typically a square, sized to the point size of the font. The origin (coordinate 0,0)
of the emBox is set to the left edge and Roman baseline of the rect.
For example, for a 10-point font, the emBox can be a rect [L,T,R,B] of [0, -8.8, 10, 1.2].

lineGap

This value is set by the font designer, and can vary widely from font to font.
In a multi-script font, different line gaps may be suitable for different scripts;
no single value may suffice. Furthermore, different kinds of text usage for a
particular script (for example, whether Japanese text is annotated with ruby or not)
may require different line gaps.

strikethroughOffset

The strikethroughOffset value is the suggested vertical offset from the Roman baseline for a strikethrough.

Note that depending on the rotation of the line, this value is either added or subtracted from the
position of the line to find the position for the strikethrough. In a line with TextRotation.ROTATE_0,
strikethrough.y = line.y + strikethroughOffset. In a line
with TextRotation.ROTATE_90, strikethrough.x = line.x - strikethroughOffset.

When applying decorations such as strikethroughs to a TextLine, the recommended procedure is to specify
an eventMirror on the ContentElement which is to receive the decoration.
In response to the Event.ADDED event, the bounds of the
TextLineMirrorRegion can be used in conjunction
with the strikethroughOffset to place the strikethrough.

underlineOffset

The underlineOffset value is the suggested vertical offset from the Roman baseline for an underline.

Note that depending on the rotation of the line, this value is either added or subtracted from the
position of the line to find the position for the underline. In a line with TextRotation.ROTATE_0,
underline.y = line.y + underlineOffset. In a line
with TextRotation.ROTATE_90, underline.x = line.x - underlineOffset.

When applying decorations such as underlines to a TextLine, the recommended procedure is to specify
an eventMirror on the ContentElement which is to receive the decoration.
In response to the Event.ADDED event, the bounds of the
TextLineMirrorRegion can be used in conjunction
with the underlineOffset to place the underline.

Creates a FontMetrics object. The FontMetrics object contains information about
the metrics of a font in an element format.
The flash.text.engine.ElementFormat.getFontMetrics() method returns objects of this class.